A conventional guardrail used on a road is configured to have pillars fixed to the ground so that shock-absorbing effects upon the occurrence of collisions are not exerted well to cause frequent human life damages, and further, connection members are broken when accidents happen, which often leads to large-scale accidents. In conventional practices, on the other hand, a guardrail has been proposed to have double foldable collision parts disposed thereon to perform shock absorption, but in this case, a plurality of fixed pillars is located to cause the shock-absorbing effects to become weak. In addition, most of steel guardrails are fixed to the ground by means of concrete blocks, so that it is hard to install the guardrails and change the positions of the installed guardrails, long construction duration is needed, and an installation cost is increased. Contrarily, a plastic barrier having specific stiffness is weak in rigidity so that there is a limit in application of a road and accordingly, it is used only in a restricted section of the road.